Abstract:Recent studies report declines in biomass, abundance and diversity of terrestrial insect groups. While anthropogenic land use is one likely contributor to this decline, studies assessing land cover as a driver of insect dynamics are rare and mostly restricted in spatial scale and types of land cover. In this study, we used rooftop-mounted car nets in a citizen science project (‘InsectMobile’) to allow for large-scale geographic sampling of flying insects across Denmark and parts of Germany. Citizen scientists … Show more
“…We detected reduced insect biomass in trap locations surrounded predominantly by forests. This result is in contrast to previous work, albeit using different sampling methods, showing high Lepidoptera biomass coming to light traps in forests compared to other land use types in the UK (Macgregor et al 2019), and higher flying insect biomass with increasing forest cover in a study using car-mounted nets in Denmark (Svenningsen et al 2020). Our malaisetrapping methods are more directed toward Hymenoptera and Diptera, and towards the lower canopy, potentially contributing to this discrepancy.…”
Section: Land Covercontrasting
confidence: 99%
“…Heavily human modified landscapes come with associated pressures, such as eutrophication and pesticide use with agricultural intensification (Goulson et al 2018, Carvalheiro et al 2020, and light pollution from urban environments (Owens et al 2020). Urban land cover can result in declines of both insect diversity (Fenoglio et al 2020, Piano et al 2020, and biomass (Macgregor et al 2019, Svenningsen et al 2020.…”
Using data from the first year of a new, long-term, standardized German Malaise Trap Program coordinated by the German Long-Term Ecological Research network, we apply an ecological gradients approach to examine the effects of climate and land cover on flying insect biomass. We hypothesized that biomass would display a unimodal relationship with temperature, consistent with thermal performance theory, would decrease with precipitation due to reduced flying activity, and would decrease in areas with more heavily human-modified land cover. Flying insect biomass was quantified from malaise traps at 84 locations across Germany throughout the 2019 growing season. We used an AICc approach to parse drivers of temperature, deviation in 2019 temperature from long-term averages, precipitation, land cover, geographic coordinates, elevation, and sampling period. We further examined how effects of temperature on insect biomass change across space by testing for interactions between temperature and latitude. Flying insect biomass increased linearly with monthly temperature across all samples. However, positive effects of temperature on flying insect biomass declined with latitude, suggesting the warm 2019 summer temperatures in southern Germany may have exceeded local insect optimums, and highlighting the spatial variation in climate change-driven impacts on insect communities. Land cover explained less variation in insect biomass, with the largest effect being lower biomass in forested sites. Future work from this newly begun German Malaise Trap Program will add a multi-year dimension to this large-scale, distributed sampling network, with the aim of disentangling the roles of multiple drivers on flying insect communities.
“…We detected reduced insect biomass in trap locations surrounded predominantly by forests. This result is in contrast to previous work, albeit using different sampling methods, showing high Lepidoptera biomass coming to light traps in forests compared to other land use types in the UK (Macgregor et al 2019), and higher flying insect biomass with increasing forest cover in a study using car-mounted nets in Denmark (Svenningsen et al 2020). Our malaisetrapping methods are more directed toward Hymenoptera and Diptera, and towards the lower canopy, potentially contributing to this discrepancy.…”
Section: Land Covercontrasting
confidence: 99%
“…Heavily human modified landscapes come with associated pressures, such as eutrophication and pesticide use with agricultural intensification (Goulson et al 2018, Carvalheiro et al 2020, and light pollution from urban environments (Owens et al 2020). Urban land cover can result in declines of both insect diversity (Fenoglio et al 2020, Piano et al 2020, and biomass (Macgregor et al 2019, Svenningsen et al 2020.…”
Using data from the first year of a new, long-term, standardized German Malaise Trap Program coordinated by the German Long-Term Ecological Research network, we apply an ecological gradients approach to examine the effects of climate and land cover on flying insect biomass. We hypothesized that biomass would display a unimodal relationship with temperature, consistent with thermal performance theory, would decrease with precipitation due to reduced flying activity, and would decrease in areas with more heavily human-modified land cover. Flying insect biomass was quantified from malaise traps at 84 locations across Germany throughout the 2019 growing season. We used an AICc approach to parse drivers of temperature, deviation in 2019 temperature from long-term averages, precipitation, land cover, geographic coordinates, elevation, and sampling period. We further examined how effects of temperature on insect biomass change across space by testing for interactions between temperature and latitude. Flying insect biomass increased linearly with monthly temperature across all samples. However, positive effects of temperature on flying insect biomass declined with latitude, suggesting the warm 2019 summer temperatures in southern Germany may have exceeded local insect optimums, and highlighting the spatial variation in climate change-driven impacts on insect communities. Land cover explained less variation in insect biomass, with the largest effect being lower biomass in forested sites. Future work from this newly begun German Malaise Trap Program will add a multi-year dimension to this large-scale, distributed sampling network, with the aim of disentangling the roles of multiple drivers on flying insect communities.
“…pollen data, farmland-specific variables, e.g. pesticide use and crop type, and proportional land cover [ 25 ], further trends may be detected with a higher degree of explained variation.…”
Section: Discussionmentioning
confidence: 99%
“…Bulk insect samples were placed in 96% ethanol and stored in a −20°C chest freezer prior to DNA extraction. Further information on the car net design, citizen science sampling, route design and environmental variables can be found in Svenningsen et al [ 25 ] and electronic supplementary material, SI. Figure 1 Observed total insect richness and hoverfly richness across biogeographic regions in Denmark.…”
Monitoring insects across space and time is challenging, due to their vast taxonomic and functional diversity. This study demonstrates how nets mounted on rooftops of cars (car nets) and DNA metabarcoding can be applied to sample flying insect richness and diversity across large spatial scales within a limited time period. During June 2018, 365 car net samples were collected by 151 volunteers during two daily time intervals on 218 routes in Denmark. Insect bulk samples were processed with a DNA metabarcoding protocol to estimate taxonomic composition, and the results were compared to known flying insect richness and occurrence data. Insect and hoverfly richness and diversity were assessed across biogeographic regions and dominant land cover types. We detected 15 out of 19 flying insect orders present in Denmark, with high proportions of especially Diptera compared to Danish estimates, and lower insect richness and diversity in urbanized areas. We detected 319 species not known for Denmark and 174 species assessed in the Danish Red List. Our results indicate that the methodology can assess the flying insect fauna at large spatial scales to a wide extent, but may be, like other methods, biased towards certain insect orders.
“…Another caveat is that since sampling is carried out using cars, roads have to be present and in good condition. Driving speed and the number of stops may have an impact on how many insects are sampled (41) and therefore requires routes to be designed with considerations of stops, turns and road conditions. For example, urban areas have a higher number of stop signs, road crossings etc.…”
Insect diversity and abundance are increasingly reported as being under pressure. However, monitoring insects across space and time is challenging, due to their vast taxonomic and functional diversity. This study demonstrates how nets mounted on rooftops of cars (car nets) and DNA metabarcoding can be applied to sample flying insect diversity across a large spatial scale within a limited time period.During June 2018, 365 car net samples were collected by 151 volunteers during two daily time intervals on 218 routes in Denmark. Insect bulk samples were processed with a DNA metabarcoding protocol to estimate taxonomic composition, and the results were compared to known flying insect diversity and occurrence data.We detected 15 out of 19 flying insect orders present in Denmark. Diptera. Psocoptera and Thysanoptera were overrepresented, while Hymenoptera, Coleoptera, Lepidoptera, Trichoptera, Odonata, Neuroptera and Plecoptera were underrepresented, compared to Danish estimates. We detected 319 species not known for Denmark. Our results indicate that this method can assess the flying insect fauna to a wide extent, but may be, like other methods, biased towards certain insect orders. Furthermore, car net sampling and DNA metabarcoding can update species records for Denmark while preserving specimens for natural history collections.
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